What is this kanji’s radical?
Someone who laughs over radicals will eventually cry over radicals.
I remember all of the radicals.
Picture the part of your body that makes up your neck. Are you picturing it? That's a building block that makes up your body. A really important one. If you didn't have that neck, you wouldn't look like a person at all. Sound familiar? It should! Because that part of your neck is a radical! Just like part of your neck is a building block of your body, the radical is a building block of kanji. Get it? I sure hope so!
This is a jukugo word that uses the on'yomi readings of the kanji. You haven't learned this reading for 首 yet, so here's a mnemonic to help you:
When you need a radical to make a new kanji, you just press a button and the radical comes tumbling down the radical chute (しゅ). There's definitely no rhyme or reason to radical picking, it's just whatever pops out of the ol' chute.